Construct Complete Binary Tree Problem Statement

Given an array or list 'ARR' containing values for 'N' nodes of a binary tree, your task is to construct a complete binary tree in a level order fashion. The elements will be filled in level-by-level starting from level 0.

A Complete Binary Tree is defined such that all levels are fully filled except, possibly, the last one, which should be filled from left to right as much as possible.

Example:

Input:

ARR = [5, 6, 10, 2, 3, 5, 9]

Output:

5 6 10 2 3 5 9 -1 -1 -1 -1 -1 -1 -1 -1

Explanation:

The binary tree constructed from the provided array would look like this:

• Level 1: The root node is 4.
• Level 2: The left child of 5 is 6; the right child of 5 is 10.
• Level 3: The left child of 6 is 2; the right child of 6 is 3; the left child of 10 is 5; the right child of 10 is 9.
• Level 4: All children of level 3 nodes are null (-1 for each).

Output is written as a single line with values separated by spaces. The tree traversal ends when all nodes at the last level are null (-1).

Constraints:

• 1 <= T <= 100
• 1 <= N <= 3000
• 0 <= ARR[i] <= 10^6
• Time limit: 1 sec

Note:

You do not need to print anything; it is already managed. Implement the function to return the root of the binary tree.